Melt the butter in a large sauté pan. Add the leeks and chopped broccolini and sauté for 15 minutes.

Add the spiralized potatoes, and toss into the leeks and broccolini until thoroughly mixed. You can use either tongs or a metal spoon to do this. Stir the milk, paprika, salt and pepper into the potatoes. Continue to cook until the liquid is absorbed, tossing the potatoes occasionally to prevent them from sticking too much to the pan, about 10 minutes.

Preheat the oven to 400˚F, placing one rack on the bottom and one rack on the top. Butter an 8" or 9" cake pan along the sides and bottom. Line with parchment paper - including the sides - and slide onto the bottom rack. Heat for 10 minutes. Remove and pile in the potato mixture. Smooth and press down firmly to thin. Slide back into the oven on the bottom rack and cook for 30 minutes, or until well browned around the edges.

Move to the top rack and broil for 2 minutes. Remove and flip the rosti out. Turn over and slide back into the cake pan. Slide back under the broiler for another minute. This can also be done with an oven-safe pan.

Garnish with thinly sliced chives, and serve warm.